Conventionally, an emulsion (EM) type silicone release coating has short chain vinyl-end silicone polymers or multiple vinyl functional silicone polymers to get fast cure with acceptable migration and also easy to be emulsified, so the base polymers have to be low viscosity to meet the manufacture process requirement. The coating is, however, difficult to provide low release force due to high cure density.
For example, U.S. Pat. No. 4,791,029A (Patent Reference 1, incorporated herein for reference) discloses aqueous emulsions of crosslinkable polyaddition organopolysiloxane compositions, comprising: a first aqueous emulsion A including end-vinylated polysiloxanes, a vinylated cyclotrisiloxane, a hydroorganodiorganopolysiloxane, a polyvinyl alcohol and a polyalkylene glycol alkyl ether or alkylphenyl ether, and a second aqueous emulsion B which comprises a catalytically effective amount of a platinum metal catalyst with siloxane polymer. The emulsions are said to be well adapted for the thin layer coating of flexible substrates to impart water-repellency and nonadherency thereto.
For example, U.S. Pat. No. 4,954,554A (Patent Reference 2, incorporated herein for reference) discloses aqueous emulsions of curable silicone compositions which provide cured coatings having improved gloss and/or water-repellancy and/or adhesive release if formulated to contain polyvinylachohol (PVA) having a degree of hydrolysis of 90 mol. % or more. The extent of improvement is directly related to the degree of hydrolysis of the PVA. PVA having an average degree of hydrolysis of from 94 to 99 mol. % is particularly effective for improving these properties of cured coatings. Conveniently, a mixture of two or more commercially available PVAs having different degrees of hydrolysis can be used to arrive at a PVA having a desired degree of hydrolysis.
For example, U.S. Pat. No. 5,095,067A (Patent Reference 3, incorporated herein for reference) discloses a release silicone emulsion composition comprising: (A) 100 parts by weight of a specific organovinylpolysiloxane; (B) from 1 to 50 parts by weight of a specific organohydrogenpolysiloxane; (C) from 0.5 part to 5 parts by weight of a platinum catalyst having a viscosity of 10 cSt or less at 25° C.; (D) from 1.5 to 15 parts by weight of a nonionic emulsifying agent having an average HLB of from 10 to 20, pH of 6.5 or less and an ionic conductance of 30 μS/cm or less; and (E) water. This composition is said to have good pot life and curability. The cured film had good release properties and residual adhesive properties of adhesives.
For example, U.S. Pat. No. 5,777,017A (Patent Reference 4, incorporated herein for reference) discloses aqueous organopolysiloxane emulsions, especially those which can be crosslinked by addition of Si-bonded hydrogen onto aliphatic multiple bond, their preparation with an emulsifier combination comprising alkylphenyl polyglycol ether and polyvinyl alcohol with a low degree of hydrolysis, and their use for preparing anti-adhesive coatings.
For example, US 20110287267A1 (Patent Reference 5, incorporated herein for reference) discloses a solventless cured release coating-forming organopolysiloxane composition having a viscosity at 25° C. of 50 to 2,000 mPa·s comprising (A) 100 weight parts of an alkenyl-functional diorganopolysiloxane that has a viscosity of 25 to 1,000 mPa·s; (B) 0.5 to 15 weight parts of a diorganopolysiloxane that has a viscosity of at least 10,000 mPa·s and that has an aliphatically unsaturated group content of no more than 0.1 mole %; (C) 0.5 to 5 weight parts of a branched organopolysiloxane that has more than one SiO4/2 unit and that is a polymer product provided by an equilibration polymerization between a branched organosiloxane oligomer represented by the average siloxane unit formula (1) (SiO4/2)(RaRb2SiO1/2)x and a diorganosiloxane oligomer; (D) a specific amount of an organohydrogenpolysiloxane that has a viscosity of 1 to 1,000 mPa·s; and (E) a hydrosilylation reaction catalyst in a catalytic quantity. The resulting cured coating is said to exhibit an excellent release performance to tacky substances and a smooth slipperiness.
For example, U.S. Pat. No. 4,870,149A (Patent Reference 6, incorporated herein for reference) discloses a solventless, cured release coating-forming organopolysiloxane composition comprising (A) 100 parts of an organopolysiloxane fluid having a branched structure and comprising (i) the siloxane unit represented by the formula SiO4/2, (ii) the siloxane unit represented by the general formula R2SiO2/2, and (iii) the siloxane unit represented by the general formula RaR2SiO1/2; (B) 0.5 to 15 parts of a diorganopolysiloxane with the average structural formula RaRc2SiO(RbRcSiO2/2)n1(Rc2SiO2/2)n2SiRc2Ra; (C) a prescribed quantity of an organohydrogenpolysiloxane; and (D) a hydrosilylation reaction catalyst. Also, a sheet-form substrate has a cured coating from this solventless, cured release coating-forming organopolysiloxane composition.
However, the above Patent References 1-6 fail to well solve the above technical problem of the prior art. Particularly, Patent References 1-4, which relate to aqueous emulsions, cannot provide a low release force emulsion silicone release coating; and Patent References 5-6, which relate to solventless, cured release coating-forming organopolysiloxane composition, obviously cannot meet the requirement on aqueous emulsions.
Therefore, there still exists a need in the art for obtaining an aqueous emulsion type silicone release coating composition which can provide a lower release force at same coat weight (CW) to sticky adhesive and possessing excellent properties including high-speed cure, cured layer with low migration, slippery & good smooth touch of the coating surface, and good anchorage to the substrate.